Batch and heap bioleaching of uranium from contaminated sediments of a natural wetland

PRETZ, FLORENCIA; MARIA BELÉN PRADOS; CURUTCHET, GUSTAVO

Simposio; 7 ISEBE. The 5th International Symposium on Environmental Biotrechnology and Engineering; 2024

Bioelectrochemical systems (BES) represent a technological platform capable of ex-ploiting microbial oxidation-reduction mechanisms for different purposes, mainly the conversion of wastewater into a renewable energy source. These systems are based on the ability of electrogenic microorganisms to transfer electrons to a solid surface, such as an electrode in an electrochemical cell, while oxidizing organic compounds. In this project, we seek to contribute to BES applications through the production of novel electrodes. The method consists of the reduction of graphene oxide (GO) and self-assembly of an hydrogel (GH) catalyzed by the metabolic activity of electrogenic microorganisms. These hydrogels could be employed as process specific electrodes, depending on the bacterial strain that catalyzed its synthesis.In this work, we explored several combinations of culture media and bacterial strains that could promote GH synthesis. Culture media were: (1) a rich medium (triptone, peptone and yeast extract); (2) a minimal medium supplemented with minerals, vita-mins, acetate-Na (electron and carbon source) and fumarate-Na 35 mM or (3) 3.5 mM and (4) the same minimal media as in (2) with the addition of lactate-Na. Bacterial strains tested were Shewanella sp., Aeromonas sp. (both strains isolated by us from an electrogenic community selected from a polluted river sediment, Reconquista, Ar-gentina) and M4 (electrogenic community selected from a polluted wetland, Río Ne-gro, Argentina). Sterile vials were filled with culture media (Vf=10 mL), inoculated with 10% of a bacterial culture (OD600≈0.3) in the presence or abscence of GO (0.14 mg/mL). Control vials in the absence of bacteria or in the presence of a sterylized bac-terial culture were prepared. Vials were flushed with ultrapure N2:CO2 (80:20) to re-move oxygen and cultured at 30ºC in an incubator. GO reduction was studied by vi-sual inspection (GO changes from brown to black) to avoid hydrogel disruption. The hydrogels were characterized when the structure was stable by scanning electron microscopy (SEM), Raman and Fourier-transformed infrared spectroscopy (FTIR).At 24, 48 and 120 h GO reduction was observed in every culture condition with She-wanella sp., M4 and Aeromonas sp., respectively. The formation of a hydrogel was evidenced after 7 days, when Shewanella sp. and M4 were grown in the presence of fumarate 35 mM and it was stable 7 days later (invertion test). In fumarate 3,5 mM, the formation of the hydrogel was evidenced after 15 days. In the absence of fumarate and in the rich medium, a colloidal reduced GO was observed even after 30 days of culture with Shewanella sp. and M4. This same result was observed with Aeromonas sp. in every tested condition. The Raman and FTIR spectra of the hydrogels were si-milar to that obtained with a chemically reduced graphene oxide, thus confirming GO reduction by bacteria. A 3D-architecture with bacteria inside a macroporous structure was observed by SEM. We are currently studying the performance of these GH as electrodes in BES.